code: def test_rmse(self):
      self.helper_test_multivariate_duplication_equality(metrics.rmse)
      self.helper_test_multiple_ts_duplication_equality(metrics.rmse)
  
      assert (
          round(
              abs(
                  metrics.rmse(
                      self.series1.append(self.series2b),
                      self.series2.append(self.series1b),
                  )
                  - metrics.mse(
                      self.series12,
                      self.series21,
                      reduction=(lambda x: np.sqrt(np.mean(x))),
                  )
              ),
              7,
          )
          == 0
      )
      self.helper_test_nan(metrics.rmse)
  
imports: import numpy
  import pandas
  import pytest
  from darts import TimeSeries
  from darts.metrics import metrics
label_desc: Use image node_id 13 for calling the TestMetrics obj's underlying member method code with example usage: obj.test_rmse() without return types